Year Number 2004 0.140641778707504 2005 1.23957788944244 2006 0.905649721622467 2007 0.719497740268707 2008 0.434909999370575 2009 0.49756196141243 2010 0.321675181388855 2011 0.351851403713226 2012 0.342154562473297 2013 0.321960687637329 2014 0.357046246528625 2015 0.275838017463684 2016 0.259495288133621 2017 0.263444691896439 2018 0.304560840129852 2019 0.274758160114288 2020 0.345437973737717 2021 0.343585729598999 2022 0.348867624998093